Method of and means for sharpening twist drills



June 10, 1969 v BELOUSOV ET AL 3,448,545

ENING TWIST DRILLS METHOD OF- AND MEANS FOR SHARP Sheet Z of 3 FiledSept. 23, 1965 June-10,1969 v ousov ET AL 3,448,545

METHOD OF AND MEANS FOR SHARRENING TWIST DRILLS Sheet 2 of 3' FiledSept. 23, 1965 INVEN roRs. Viral/e Belousov Const-Jean Alecsandrescu BYGheorghe Zmau Mihif' Sfan ow June 10, 1969 v. BELOUSOV ET AL 3,448,545

METHOD OF AND MEANS FOR SHARPENING TWIST'-DRILLS Sheet 3 of 5 FiledSept. 25, 19651 FIG. 3A

Vi fall's Belousov Const--Jean Alecsandrescu Gheorghe Zmau M11151}; SfanINVEN IORS FIG. 3C

United States Patent US. C]. 51-73 8 Claims ABSTRACT OF THE DISCLOSURE Atwist drill is sharpened by reciprocating it generally rectilineally ina plane passing through the drill axis and along a line including anangle of 40 to 50 with that axis while holding the tip of the drillagainst a cup-shaped grinding wheel rotating about an axis which is skewto the drill axis and includes with the aforementioned plane an angle of40 to 50.

Our present invention relates to a method of sharpening twist drills andto a machine for carrying out this method.

Conventional drill-sharpening technique utilizes flat, cylindrical orconical grinding disks or wheels executing relatively complex motionswith reference to the drill to be sharpened. With the use of acup-shaped grinding wheel having a frustoconical inner periphery, forexample, each end face or land of the drill may be given its generallyconical shape by letting the axis of the rotating wheel revolve aboutthe tip of the drill which comes into contact with the abrasive wheeledge once per revolution. At the moment of contact the drill axisintersects the wheel axis at an acute angle whose magnitude, togetherwith that of the vertex angle of the frustum, determines the apex angleof the drill at the junction of its lands; it is therefore necessary tomaintain the proper shape of the fnustoconical grinding-wheel surface bytrueing it with the aid of a diamond whenever it is deformed by wear.

The general object of our invention is to provide a method of and meansfor sharpening twist drills in a more efiicient manner and withelimination of such trueing step.

This object is realized, pursuant to our invention, by positioning thedrill with its axis skew to the axis of a cup-shaped grinding wheel andrelatively reciprocating the wheel and the drill with a generallyrectilineal motion in a plane containing the drill axis and in adirection which includes an acute angle, with the drill axis, the wheelaxis also including an acute angle of preferably 40 to 50 with theaforesaid plane. During this reciprocating motion, the tip of the drillis periodically engaged by an inner peripheral edge of the wheel along acontact area which is part of an elliptical cylinder; this imparts tothe engaged land of the drill an elliptically cylindrical curvaturedefining a cutting edge which is much more efiicient than thatobtainable by standard techniques so that the service life of the drillis three to six times as long as that of drills conventionallysharpened. Furthermore, since the same circular edge sweeps the entiresurface of the land, there is no longer any need for trueing theabrasive face of the grinding wheel.

The relative reciprocation between the wheel motion and the drillsupport need not be exactly rectilineal but can proceed along an arc ofa circle of large radius approximating a straight line; thus, a machinefor carrying out the aforedescribed method may include a crank drive foroscillating a supporting arm about a fulcrum remote 3,448,545 PatentedJune 10, 1969 from the region of contact between the drill and thegrinding Wheel.

The invention will be described in greater detail with reference to theaccompanying drawing in which;

FIG. 1A is a perspective view of a grinding wheel and a drillcooperating therewith in accordance with the invention;

FIG. 1B is a view similar to FIG. 1, showing the drill and the wheelfrom a different angle;

FIG. 2 is another view generally similar to FIG. 1A, illustrating afurther aspect of our improved grinding method;

FIG. 3A is a side-elevational view of a machine for carrying out themethod of FIGSAlA-IC;

FIG. 3B is an end-elevational view of the machine of FIG. 3A, with adrill imposition thereon; and

FIG. 3C is a top view of the machine without the drill and its mounting.

In FIGS. 1A and 1B we have shown a cup-shaped grinding wheel 1 rotatableabout an axis Q as indicated by arrow A, the wheel having a circular rim3 centered on axis Q. The concave side of rim 3, which is of generallyfrustoconical shape, is in contact with a land 16 of a twist drill 2having an axis N skew to the wheel axis Q, the wheel 1 and the drill 2being relatively oscillated in a direction B which includes an angle '0with drill axis N. During this relative reciprocation, the rim portion 3of wheel 1 engages the land 16 of drill 2 along part of the periphery ofan imaginary elliptical cylinder 4 whose axis M is parallel to thedirection B, the intersection of this cylinder with any planeperpendicularly to axis Q having the shape of a circle whose radius a(FIG. 2) is that of the inner edge 3' of Tim 3. As the wheel rotates inthe direction A, edge 3' periodically sweeps across land 16 to give itan elliptically cylindrical shape. At the same time, any irregularitiesdeveloping along the substantially frustoconical rim surface areautomatically evened out by the linear contact between the land 16 andthe inner wheel periphery as the drill 2 is slowly advanced along itsaxis N, to the extent dictated by the desired depth of grind, asindicated by arrow C. As will likewise be apparent from FIG. 1A, theouter edge 3 and adjacent portions of rim 3 curve away from the cylinder4 so as not to participate in the sharpening process proper which isperformed exclusively by the inner edge 3'. After the land 16 has beensuitably sharpened, the drill 2 may be axially retracted and rotatedthrough for a sharpening of the opposite land 16.

As illustrated in FIG. 2, a generally toroidal transition zone 18 may beformed between the land 16 and the adjoining drill flank 17 byrelatively rotating the wheel 1 and the drill 2 in a direction B alongan arc centered on .a point 0 which is relatively close to the point ofcontact between drill 2 and wheel rim 3. On the other hand, as describedhereinafter with reference to FIGS. 3A-3C, the rectilineal reciprocationB may be replaced in practice by an oscillation around an arc whosecenter is relatively remote from that point of contact.

If the lands 16, 16" .are to converge at a pyramidal point, the drill 2may be laterally displaced (arrow D, FIG. IE) to change the location ofits point of contact with wheel 1, with corresponding modification ofthe shape of the drill tip. If the cutting edge of each land is to bedivided into two or three segments inclined at different angles, thismay be accomplished by varying the angle of inclination a of drill axisQ with reference to the direction of reciprocation B.

A machine for performing the grinding operation described above has beenillustrated in FIGS. 3A, 3B and 3C. It comprises a base 20 having an arm21 which supports a driving unit for the grinding wheel 1, this unitincluding a motor 22 and a transmission belt 23. The shaft of wheel 1 isjournaled in a bearing sleeve 25 held in a clamp 26. Mounting arm 21 isswingable about a fulcrum 24 and is integral with an arm 8 linked at 27with a pitman 7 reciprocated by a crank pin 28 under the control of adrive motor via a transmission belt '6. The position of coupling 27along arm 8 is adjustable in a slot 29 thereof to vary the effectivestroke length of oscillation B which, of course, must be sufficient tocarry the working edge 3' across the entire land 16 or 16 (FIG. 1A).

A bracket 30 on base 20 supports a shaft 11 which is rotatable, asindicated by arrow C, and carries a chuck 10 holding the drill 2 to besharpened. A pair of handles 12, 13 are joined to shaft 11 at oppositesides of a yieldable coupling 31. In order to bring the drill 2 upagainst the wheel 1, handle 12 may be swung in the direction C for rapidengagement of the drill with the wheel whereupon this handle may beimmobilized by an adjustable detent and handle 13 may be actuated tocontinue the axial advance of the drill at a reduced rate. If the wheel1 requires readjustment after a certain amount of wear,

clamp 26 as opened by the release of a locking lever 14 and the wheel isaxially shifted by rotation of a lever 15 which is connected with thejournal 25 of the wheel shaft through a rack-and-pinion drive not shown.

Arrow B" in FIG. 3A represents the aforedescribed arcuate oscillationabout fulcrum 24 which replaces the linear oscillation B illustrated inFIGS. 1A and 2. This oscillation, as best seen in FIG. 3B, takes placein a vertical plane P which also contains the axis of drill 2. Thegeneral direction of the oscillatory motion B" is represented in FIG. 3Aby a horizontal line H. The angle of elevation of wheel axis Q withreference to the level H has been shown at a in FIG. 3A and may rangebetween 40 and 50. A similar angle b is shown in FIG. BC to to includedbetween wheel axis Q and plane P.

We have found that, by the use of our improved method and machine, thetime for sharpening medium-sized drills can be reduced by 10 to seconds.The operation may be performed without cooling and, for reasons alreadyset forth, does not require any reshaping of the abrasive wheel surfaceby a diamond inasmuch as the working edge 3' is invariably defined bythe inner diameter d (FIG. 2) of the cylindrical wheel portion. Therapid/ slow positioning device 11-13 speeds up the ancillary operations,such as the rotation of the drill chuck 10 through 180 after thegrinding of the first land. Moreover, the shape of the cutting faces ofthe drill may be widely varied by suitable choice of the relativepositions of the drill and the wheel.

We claim:

1. A method of sharpening twist drills by means of a cup-shaped grindingwheel having an annular edge centered on an axis of rotation, comprisingthe steps of rotating said wheel about said axis of rotation, holding anend face of a twist drill against the concave side of said annular edgewhile positioning the drill with its axis skew to said axis of rotation,and relatively reciprocating said drill and said wheel with a generallyrectilineal motion in a plane containing the drill axis and in adirection which includes a first acute angle with said drill axis, saidaxis of rotation including a second acute angle with said plane.

2. A method as defined in claim 1 wherein said second acute angle rangesbetween 40 and 50.

3. A method as defined in claim 1 wherein said drill is advanced alongits axis toward said wheel at a rate which is slow compared with therate of reciprocating motion.

4. A machine for sharpening twist drills, comprising a cup-shapedgrinding wheel with an annular edge centered on an axis of rotation;mounting means journaling said wheel for rotation about said axis; firstdrive means for so rotating said wheel; supporting means for holding anend face of a drill against the concave side of said edge of saidgrinding wheel while maintaining the drill axis skew to said axis ofrotation; second drive means for relatively oscillating said supportingmeans and said mounting means with a generally arcuate motion with along radius in a plane containing the drill axis and in a directionincluding a first acute angle with said drill axis, said axis ofrotation including a second acute angle with said plane; and feed meansfor relatively advancing said mounting means and said supporting meanstoward each other along said drill axis.

5. A machine as defined in claim 4 wherein said second drive meanscomprises a s wingable support for said mounting means, said supporthaving a fulcrum remote from said end face.

6. A machine as defined in claim 5 wherein said second drive meansfurther includes a crank drive forming a junction with said arm andstroke-adjusting means for varying the distance of said junction fromsaid fulcrum.

7. A machine as defined in claim 4 wherein said second acute angleranges between 40 and 50.

8. A machine as defined in claim 4 wherein said feed means comprises afirst operating member for rapidly moving said drill into contact withsaid wheel and a second operating member actuatable in an arrestedposition of said first operating member for slowly advancing said drillalong its axis.

References Cited UNITED STATES PATENTS 270,365 1/18'83 Bancroft 51 2l92,017,532 10/1935 Elter 51-219 X 2,512,888 6/1950 Douglas 51-219 X3,020,680 2/1962 Soderman 5l73 3,178,857 4/1965 Grob 51-219 X 3,200,5408/ 1965 Lavallee 51-73 FOREIGN PATENTS 1,006,695 1/ 1952 France.

161,637 7/1964 U.S.S.R.

HAROLD D. WHITEHEAD, Primary Examiner.

Us. 01. X.R. s1 219, 288

